#include <fstream>
#include <algorithm>
using namespace std;
ifstream cin("heavymetal.in");
ofstream cout("heavymetal.out");
const int MAX = 100001;
struct interval {
    int st, dr;
} v[MAX];
int n, dp[MAX];
bool cmp(interval a, interval b) {
    return a.dr < b.dr;
}
int main()
{
    cin >> n;
    for(int i = 1; i <= n; ++i) {
        cin >> v[i].st >> v[i].dr;
    }
    sort(v + 1, v + n + 1, cmp);
    for(int i = 1; i <= n; ++i) {
        dp[i] = dp[i - 1];
        int st = 1, dr = i - 1;
        while(st <= dr) {
            int mij = (st + dr) / 2;
            if(v[mij].dr <= v[i].st) {
                st = mij + 1;
            } else {
                dr = mij - 1;
            }
        }
        if(dp[dr] + v[i].dr - v[i].st > dp[i]) {
            dp[i] = dp[dr] + v[i].dr - v[i].st;
        }
    }
    cout << dp[n];
    return 0;
}